Abstract

We investigate the near-field optical coupling between a single semiconductor nanocrystal (quantum dot) and a nanometer-scale plasmonic metal resonator using rigorous electrodynamic simulations. Our calculations show that the quantum dot produces a dip in both the extinction and scattering spectra of the surface-plasmon resonator, with a particularly strong change for the scattering spectrum. A phenomenological coupled-oscillator model is used to fit the calculation results and provide physical insight, revealing the roles of Fano interference and hybridization. The results indicate that it is possible to achieve nearly complete transparency as well as enter the strong-coupling regime for a single quantum dot in the near field of a metal nanostructure.

Figures (5)

Illustration of the quantum-dot / metal-nanoparticle hybrid system considered. The blue ellipses represent silver nanoparticles and the red circle represents a semiconductor nanocrystal. The various domains used in the finite-difference time-domain simulations are also illustrated.

Extinction and scattering spectra for a quantum-dot / metal-nanoparticle hybrid system. The structure is illustrated in the inset of (a). Solid squares are values of (a) extinction cross-section (in thousands of nm2) for quantum-dot linewidth γQD = 10 meV, (b) scattering cross-section for γQD = 10 meV, (c) extinction for γQD = 2 meV, and (d) scattering for γQD = 2 meV, all calculated using a rigorous finite-difference time-domain (FDTD) method. The solid lines are fits to a phenomenological coupled-oscillator model [Eq. (7) and Eq. (8)]. Solid circles are extinction and scattering spectra for the same system but without quantum-dot absorption, also calculated by the FDTD method.

(a) and (c): Peak-to-peak separation for extinction and scattering spectra, respectively, according to a coupled-oscillator model [Eq. (9) and Eq. (10)]. Values are shown as a function of quantum-dot linewidth, γQD, and coupling strength, g, with both values normalized by the surface-plasmon linewidth, γSP. (b) and (d) Depth of the transparency dip in the extinction and scattering spectra, normalized by the height of the plasmon-resonance peak, according to the same coupled-oscillator model.

Electric field, Ez, and cosine of its phase, cos(Φ), for the quantum-dot / metal-nanoparticle structure shown in Fig. 1, calculated using the rigorous finite-difference time-domain method. The z direction is along the long axes of the metal nanoparticles. Results are shown at the surface-plasmon resonance energy with (b,d) and without (a,c) the quantum-dot absorption.

(a) Illustration of a quantum-dot / metal-nanoparticle hybrid structure that could potentially be fabricated lithographically. (b) Extinction spectra for the structure when the corners of the metal nanoparticles have a radius of curvature of 5 nm (solid squares) and 2 nm (open squares), calculated using the rigorous finite-difference time-domain (FDTD) method. The lines are fits to Eq. (7). (c) Scattering spectra for the same structures, also calculated by the FDTD method. The lines are fits to Eq. (8).